Cloud manufacturing (CMfg) is a new manufacturing paradigm over computer networks aiming at using distributed resources in the form of manufacturing capabilities, hardware, and software. Some modern technologies such as cloud computing, Internet of Things (IoT), service-oriented, and radio-frequency identification (RFID) play a key role in CMfg. In CMfg, all resources needed for manufacturing such as hardware, software, and manufacturing capabilities are virtualized; the services are provided by manufacturing resources. In this paper, the key characteristics, concepts, challenges, open issues, and future trends of cloud manufacturing are presented to direct the future researches. Accordingly, five directions of advances in CMfg are introduced and the articles in five categories are reviewed and analyzed: (1) studies focused on the architecture and platform design of CMfg; (2) studies concentrated on resource description and encapsulation; (3) studies focused on service selection and composition; (4) studies aimed at resource allocation and service scheduling; and (5) studies aimed at service searching and matching. The article also aims at providing a development diagram in the area of CMfg as a roadmap for future research opportunities and practice.